Re: [PATCH 3/6] devfreq: add support for suspend/resume of a devfreq device

[Chanwoo Choi <cw00.choi@samsung.com>]

Hi Lukasz,

I add the one more comment for devfreq_resume_device()

On 2018년 11월 23일 19:01, Lukasz Luba wrote:
> Hi Chanwoo Choi,
> 
> On 11/23/18 12:54 AM, Chanwoo Choi wrote:
>> Hi Lukasz,
>>
>> I add one more comment about devfreq_resume_device().
>>
>> On 2018년 11월 22일 20:00, Lukasz Luba wrote:
>>>
>>>
>>> On 11/22/18 3:58 AM, Chanwoo Choi wrote:
>>>> On 2018년 11월 22일 03:01, Lukasz Luba wrote:
>>>>> The patch adds support for handling suspend/resume process.
>>>>> It uses atomic variables to make sure no race condition
>>>>> affects the process.
>>>>>
>>>>> The patch draws on Tobias Jakobi's work posted ~2 years ago, who tried to
>>>>> solve issue with devfreq device's frequency during suspend/resume.
>>>>> During the discussion on LKML some corner cases and comments appeared
>>>>> related to the design. This patch address them keeping in mind suggestions
>>>>> from Chanwoo Choi.
>>>>
>>>> Please remove the duplicate information about patch history.
>>>>
>>>>>
>>>>> Suggested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
>>>>> Suggested-by: Chanwoo Choi <cw00.choi@samsung.com>
>>>>> Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
>>>>> ---
>>>>>    drivers/devfreq/devfreq.c | 45 +++++++++++++++++++++++++++++++++++++++------
>>>>>    1 file changed, 39 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>> index cf9c643..7e09de8 100644
>>>>> --- a/drivers/devfreq/devfreq.c
>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>> @@ -872,14 +872,33 @@ EXPORT_SYMBOL(devm_devfreq_remove_device);
>>>>>     */
>>>>>    int devfreq_suspend_device(struct devfreq *devfreq)
>>>>>    {
>>>>> -	if (!devfreq)
>>>>> -		return -EINVAL;
>>>>> +        int ret;
>>>>
>>>> Move 'ret' definition under 'if (devfreq->suspend_freq) {'
>>>> because 'ret' is used if suspend_freq isn't zero.
>>> Not only there, 6 lines above 'ret' is used for
>>> devfreq->governor->event_handler().
>>
>> OK.
>>
>>>>
>>>>> +        unsigned long prev_freq;
>>>>> +        u32 flags = 0;
>>>>> +
>>>>> +        if (!devfreq)
>>>>> +                return -EINVAL;
>>>>> +
>>>>> +        if (devfreq->governor) {
>>>>> +		ret = devfreq->governor->event_handler(devfreq,
>>>>> +					DEVFREQ_GOV_SUSPEND, NULL);
>>>>> +		if (ret)
>>>>> +			return ret;
>>>>> +	}
>>>>>    
>>>>> -	if (!devfreq->governor)
>>>>> -		return 0;
>>>>> +	if (devfreq->suspend_freq) {
>>>>> +		if (atomic_inc_return(&devfreq->suspend_count) > 1)
>>>>> +			return 0;
>>>>>    
>>>>> -	return devfreq->governor->event_handler(devfreq,
>>>>> -				DEVFREQ_GOV_SUSPEND, NULL);
>>>>> +		ret = devfreq_set_target(devfreq, devfreq->suspend_freq,
>>>>> +					 &prev_freq, flags);
>>>>
>>>> Remove the 'prev_freq' parameter.
>>> OK
>>>>
>>>>> +		if (ret)
>>>>> +			return ret;
>>>>> +
>>>>> +		devfreq->resume_freq = prev_freq;
>>>>
>>>> As I commented on patch2, if devfreq_set_taget save the current frequency
>>>> to 'devfreq->resume_freq', this line is not needed.
>>> OK
>>>>
>>>>
>>>>> +	}
>>>>> +
>>>>> +        return 0;
>>>>>    }
>>>>>    EXPORT_SYMBOL(devfreq_suspend_device);
>>>>>    
>>>>> @@ -893,9 +912,23 @@ EXPORT_SYMBOL(devfreq_suspend_device);
>>>>>     */
>>>>>    int devfreq_resume_device(struct devfreq *devfreq)
>>>>>    {
>>>>> +        int ret;
>>>>
>>>> Move 'ret' definition under 'if (devfreq->suspend_freq) {'
>>>> because 'ret' is used if suspend_freq isn't zero.
>>> OK
>>
>> If you change the devfreq_resume_device() according to my new comment,
>> please ignore it.
>>
>>>>
>>>>> +        unsigned long prev_freq;
>>>>
>>>> Remove prev_freq variable which is not used on this function.
>>>> After calling devfreq_set_target, prev_freq is not used.
>>> OK
>>>>
>>>>> +        u32 flags = 0;
>>>>> +
>>>>>    	if (!devfreq)
>>>>>    		return -EINVAL;
>>>>>    
>>>>> +	if (devfreq->suspend_freq) {

In devfreq_resume_device(), it should check the 'devfreq->resume_freq'
instead of 'devfreq->suspend_freq'.


>>>>> +		if (atomic_dec_return(&devfreq->suspend_count) >= 1)
>>>>> +			return 0;
>>>>> +
>>>>> +		ret = devfreq_set_target(devfreq, devfreq->resume_freq,
>>>>> +					 &prev_freq, flags);
>>>>
>>>> Remove the 'prev_freq' parameter.
>>> OK
>>>>
>>>>> +		if (ret)
>>>>> +			return ret;
>>>>> +	}
>>>>> +
>>>>>    	if (!devfreq->governor)
>>>>>    		return 0;
>>
>> Please change the code as following because you uses the following type
>> in the devfreq_suspend_device(). If there is any special issue, please
>> keep the same format in order to improve the readability.
>>
>> 	if (devfreq->governor) {
>> 		ret = devfreq->governor->event_handler(devfreq,
>> 				DEVFREQ_GOV_RESUME, NULL);
>> 		if (ret)
>> 			return ret;
>> 	}
>>
>>
> OK, I will change the code to keep the same format.
> Thank you for the review.
> 
> Regards,
> Lukasz
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics